What is the meaning of the escape velocity from the surface of an object (like the earth or the sun or a star)?

What is the meaning of the escape velocity from the surface of an object (like the earth or the sun or a star)? How does the escape velocity change if a given amount of mass is compressed into a smaller size? Can a given amount of mass be compressed into such a small size that the escape velocity can reach the speed of light? If so, what is the result? Why would such an object be called a black hole?